Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, tu cach
dao voi » da voi, dao noi, do voi
hieu ve » hieu va, hieu van
hoi hoc » hoa hoc, khoa hoc, hoi chuc
hoi hoi » hoc hoi, hoi doi, doi hoi
te sach » toc sach
cu tren » tu tren, dua tren
y nang » ky nang, ly nang, v nang
ve cac » va cac, vien cac
cac su » cach su, cac sau, cac du
va dao » ca dao
voi cu » voi c, hoi cu, voi co
su va » su van, tu va

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (te sach)) y nang ((hoi hoi) OR (hoi hoc)). hieu ve cac su va dao voi cu tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (te sach)) y nang ((hoi hoi) OR (hoi hoc)). hieu ve cac su va dao voi cu tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (te sach)) y nang ((hoi hoi) OR (hoi hoc)). hieu ve cac su va dao voi cu tren".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (te sach)) y nang ((hoi hoi) OR (hoi hoc)). hieu ve cac su va dao voi cu tren*.